Field of the Invention
The present invention relates to the technical field of power electronics and power systems and, more particularly to a converter valve.
Description of Related Art
A converter valve is a critical component in high voltage direct current transmission (HVDC), and has a relatively bulky physical size. In operation, the converter valve is subjected to a voltage of several hundred kV at both ends, and is in the process of frequent switching on and off. At present, a single commercial power electronics withstands a voltage of up to 8.5 kV. Accordingly, it is necessary to connect dozens of or even nearly one hundred stages of the devices in series. A valve tower generally uses a structure with a plurality of valve layers sequentially stacked from top to bottom and thyristors evenly distributed on respective valve layers.
One valve layer of the converter valve is generally composed of two valve modules. Currently, the two valve modules are connected in a split-level structure or an even-level structure. For a split-level structure arrangement, 16 reinforced epoxy resin rods are required to construct a cage-type frame in space, and then various assemblies are sequentially secured at different locations of this cage-type frame, resulting in a very complicated structure and cumbersome installation and maintenance. In addition, this cage-type frame has relatively poor shock resistance. For an even-level structure arrangement, suspending insulators are used between an upper layer and a lower layer, no connection measures are taken between two assemblies within one valve layer, and the converter valve is configured to be two independent converter valves effectively, resulting in complex installation. In addition, when external forces such as earthquake occur, displacement between valve layers is relatively large, and accordingly, there may exist a relatively large change in distance between two valve modules of the valve layer. The converter valve has a poor integrity.
In addition, a large number of components and devices are included in the valve tower for the converter valve, and it is necessary to take into consideration the convenience for repair and maintenance in later operations during the designing process. At present, there are two main ways in the maintenance of the valve tower for the converter valve. One is to operate directly on a lift truck without a maintenance platform inside the valve tower. This way can merely maintain peripheral devices of the valve tower, and interior devices of the valve tower are difficult to repair in case of failure. The other is to provide a maintenance platform inside the valve tower. The maintenance platform and the valve layer are configured in two main forms. In a first structure, each valve layer consists of two half-layer valves arranged side-by-side in a horizontal direction. The two half-layer valves are securely connected together, a maintenance platform is provided between the half-layer valves, and the maintenance platform is located on the same horizontal plane as the valve layer. Since the maintenance platform is directly connected with both half-layer valves, the maintenance platform must be wide enough in order to meet insulation requirements, which necessarily increases the area of the valve tower. In addition, the maintenance platform is parallel to the valve layer, which is not convenient for operation and maintenance staff to perform the maintenance on devices. In the other structure, each valve layer also consists of two half-layer valves. However, the two half-layer valves are in a split-level configuration, and are not on the same horizontal plane. The maintenance platform is provided at an intermediate location of the two half-layer valves in a vertical direction. The maintenance platform of such a structure has a relatively small width and the insulation requirements are met. However, it is only convenient for maintaining one of the two half-layer valves, but not for the other half-layer valve.